arithmetic without limitations

[Torbjorn Granlund]

  We will change the table representation slightly for 5.0.1 to fix the
  bug you discovered.
  
This is now in the GMP repo.

The new FFT_TABLE3 is not in many gmp-mparam.h files yet, and since the
older mechanisms have not been fixed, one may still hit the bug you
reported.

To generate new tables, use tune/tuneup, perhaps with some suitable
-f[number] argument.  It will take a while, but the new tables are
presumably very accurate.

-- 
Torbjörn